Abstract: The plant drug known as Kou-Teng, meaning "Hookclimber" consists of a portion of a branch cut above and below a node bearing usually two opposite recurved hook-like thorns obtained from a Rubiaceous plant belonging to the genus Uncaria Schreb. The hooks are modified peduncles of undeveloped inflorescences adapted to the climbing habit of the plant. Up to date, 13 species of Uncaria are found in regions south of the Yangtsze river, extending to the islands of Taiwan and Hainan. In the classical treatise on Materia Medica "Ming-I-Pieh-Lu", compiled by the eminent physician Tao Hung-ching (452-536), Kou-Teng also known as Tiao-Teng, is said to be native to the Chien-Ping district, now Wushan Hsien in Szechuan bordering Hupeh province. The commonest species in western and central China with which the drug Kou-Teng has been definitely associated is Uncaria sinensis (Oliver) Haviland. It was first technically described by D. Oliver as a species of Nauclea, based on specimens collected by A. Henry in Nantao, Hupeh, the identical region mentionod by Tao Hung-ching nearly 1500 years ago. At the time of the publication of the botanical description of Nauclea sinensis in Hooker's Icones Plantarum, vol. 2, 1891, Oliver stated on the authority of Augustine Henry, then Commissioner of Customs stationed in I-Chang, that about 20 tons of the crude drug Kou-Teng are exported from Hankow annually. In an examination of specimens obtained from drug shops in Canton, the writer came across with some fragmentary leaves still attached to the stem which proved that the crude drug passing as Kou-Teng sold in South China came from Uncaria rhynchophylla (Miq.) Jackson, not from U. sinensis (Oliver) Haviland. Subsequent investigations of several lots of the drug obtained at random confirmed this opinion. The two species are morphologically very distinct, and moreover they occupy different geographic regions; U. rhynchophylla is widely distributed in Kwangsi, Kwangtung, Hunan and Kiangsi, and U. sinensis though occurring most abundantly in Szechwan and Hupeh also extends into the outer fringes of northern Yunnan and north-eastern Kweichow. The nature and degree of potency of a drug now known to be derived from two different sources should be subjected to comparative study.